Method, apparatus, computer program, and non-transitory computer-readable medium for video encoding and decoding - Patents.com

Abstract

To provide a video coding method or the like which is executed by a decoder.SOLUTION: A method includes: determining, when it is determined if a reference block for the current block is in a different CTU (coding tree unit) than a CTU for the current block (Yes in S1302), whether it is determined if the CTU of the current block and a memory have the same size (S1306); determining, when the CTU of the current block and the reference sample memory have the same size (Yes in S1306), a first area in the CTU of the current block, the first area being collocated with a second area in the different CTU (S1308); determining whether the memory location for the reference block is available or not on the basis of a decoding state of the first area (S1310); and reading, when the memory location for the reference block is available, one or more samples from the memory location to decode the current block (S1314).SELECTED DRAWING: Figure 13

Description

[Technical field]

[0001] This disclosure describes embodiments generally relating to video coding. [Background technology]

[0002] The background description provided herein is intended to generally present the context of the present disclosure. The work of the presently named inventors is not expressly or impliedly admitted as prior art to the present disclosure to the extent that that work is described in this Background section, and any aspects of the description that may not otherwise qualify as prior art at the time of filing.

[0003] Video coding and decoding can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can include a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luminance samples and associated chrominance samples. The sequence of pictures can have a fixed or variable picture rate (commonly known as frame rate) of, for example, 60 pictures per second, or 60 Hz. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video (1920x1080 luminance sample resolution at a frame rate of 60 Hz) at 8 bits per sample requires a bandwidth approaching 1.5 Gbit / s. One hour of such video requires more than 600 Gbytes of storage space.

[0004] One goal of video coding and decoding can be the reduction of redundancy in the input video signal by compression. Compression can help reduce the above bandwidth or storage space requirements by more than two orders of magnitude in some cases. Both lossless and lossy compression as well as their combinations can be used. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be the same as the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely used. The amount of distortion that is tolerated depends on the application, for example, a user of a particular consumer streaming application may tolerate higher distortion than a user of a television distribution application. The achievable compression ratio can reflect that a higher tolerable / acceptable distortion may result in a higher compression ratio.

[0005] Motion compensation can be a lossy compression technique and can refer to a technique used for the prediction of a newly reconstructed picture or picture portion after blocks of sample data from a previously reconstructed picture or portion thereof (reference picture) are spatially shifted in a direction indicated by a motion vector (hereafter MV). In some cases, the reference picture can be the same as the picture currently being reconstructed. The MV can have two dimensions X and Y, or three dimensions, with the third dimension being an indication of the reference picture in use (the latter can indirectly be the temporal dimension).

[0006] In some video compression techniques, the MV applicable to a particular area of ​​sample data can be predicted from other MVs, e.g., from other areas of sample data that are spatially adjacent to the area being reconstructed and that precede that MV in the decoding order. Doing so can significantly reduce the amount of data required to code the MV, thereby removing redundancy and increasing compression. For example, when coding an input video signal obtained from a camera (known as natural video), MV prediction can work because there is a statistical possibility that areas larger than the area to which a single MV is applicable move in a similar direction, and therefore, in some cases, can be predicted using similar motion vectors derived from MVs of neighboring areas. As a result, the MV determined for a given area is similar or the same as the MV predicted from the surrounding MVs, and after entropy coding, can be represented with fewer bits than would be used if coding the MV directly. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., a sample stream). In other cases, the MV prediction itself can be lossy, e.g., due to rounding errors when calculating a predictor from several surrounding MVs.

[0007] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Rec. H265, “High Efficiency Video Coding”, December 2016). Among the many MV prediction mechanisms proposed by H.265, a technique hereafter referred to as “spatial merging” is described in this specification.

[0008] When the current block is decoded using intra block copy, the memory is referenced to read samples for decoding the current block. Since the size of the memory is constrained, the memory locations are overwritten when the memory is uploaded with samples from the recently decoded block. According to the new method, it is required to efficiently utilize the memory to perform intra block copy. Summary of the Invention

[0009] In accordance with an exemplary embodiment of the present disclosure, a method of video decoding for a decoder includes receiving a coded video bitstream. The method further includes determining whether a reference block for a current block is located in a coding tree unit (CTU) different from a CTU of the current block, the reference block and the current block being located in a same picture included in the coded video bitstream. The method further includes determining whether a CTU of the current block and a reference sample memory have the same size in response to determining that the reference block is located in a different CTU. The method further includes, in response to determining that the CTU of the current block and the reference sample memory have the same size, (i) determining a first area in the CTU of the current block that is co-located with a second area in a different CTU, the first area having location coordinates in the CTU of the current block that are the same as location coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location in the reference sample memory for the reference block is available based on a decoding state of the first area; and (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from a memory location corresponding to the reference block.

[0010] In accordance with an exemplary embodiment of the present disclosure, a video decoder for video decoding includes a processing circuit configured to receive a coded video bitstream, the processing circuit further configured to determine whether a reference block for a current block is located in a coding tree unit (CTU) different from a CTU of the current block, the reference block and the current block being located in a same picture included in the coded video bitstream, the processing circuit further configured to determine whether a CTU of the current block and a reference sample memory have the same size in response to determining that the reference block is located in a different CTU. The processing circuit is further configured, in response to determining that the CTU of the current block and the reference sample memory have the same size, to (i) determine a first area in the CTU of the current block that is co-located with a second area in a different CTU, the first area having location coordinates in the CTU of the current block that are the same as location coordinates of the second area in the different CTU of the reference block; (ii) determine whether a memory location in the reference sample memory for the reference block is available based on a decoding state of the first area; and (iii) in response to determining that the memory location for the reference block is available, read one or more samples for decoding the current block from a memory location corresponding to the reference block.

[0011] According to an exemplary embodiment of the present disclosure, a non-transitory computer-readable medium is provided that, when executed by a processor of a video decoder, causes the processor to perform a method. The method includes receiving a coded video bitstream. The method further includes determining whether a reference block for a current block is located in a coding tree unit (CTU) different from a CTU of the current block, the reference block and the current block being located in a same picture included in the coded video bitstream. The method further includes, in response to determining that the reference block is located in a different CTU, determining whether the CTU of the current block and the reference sample memory have the same size. The method further includes, in response to determining that the CTU of the current block and the reference sample memory have the same size, (i) determining a first area in the CTU of the current block that is co-located with a second area in a different CTU, the first area having location coordinates in the CTU of the current block that are the same as location coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location of the reference sample memory for the reference block is available based on a decoding state of the first area; and (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from a memory location corresponding to the reference block.

[0012] Further features, nature and various advantages of the disclosed subject matter will become apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic block diagram of a communication system (100) according to an embodiment. [Diagram 2] 1 is a schematic block diagram of a communication system (200) according to an embodiment. [Diagram 3]FIG. 2 is a schematic block diagram of a decoder according to an embodiment; [Figure 4] FIG. 2 is a schematic block diagram of an encoder according to an embodiment; [Diagram 5] 4 shows a block diagram of an encoder according to another embodiment. [Figure 6] 4 shows a block diagram of a decoder according to another embodiment; [Figure 7] FIG. 2 is a schematic diagram of a current block and its surrounding spatial merge candidates in one example. [Figure 8] FIG. 2 is a schematic diagram of intra-picture block compensation; [Figure 9] 1A to 1D are schematic diagrams of intra-picture block compensation with a search range of one coding tree unit (CTU) size. [Figure 10] 5A to 5D are schematic diagrams of a reference sample memory. [Figure 11] FIG. 13 is a schematic diagram of a reference block in a first CTU and a corresponding co-located block in a second CTU. [Figure 12] 13 is a schematic diagram of a reference block in a first CTU and a corresponding co-located block in a second CTU when a third CTU is present between the first CTU and the second CTU. FIG. [Figure 13] 4 illustrates an embodiment of a process performed by an encoder. [Figure 14] 4 illustrates an embodiment of a process performed by an encoder. [Figure 15] FIG. 1 is a schematic diagram of a computer system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] FIG. 1 illustrates a schematic block diagram of a communication system (100) according to an embodiment of the present disclosure. The communication system (100) includes a plurality of terminal devices that can communicate with each other via, for example, a network (150). For example, the communication system (100) includes a first pair of terminal devices (110) and (120) that are interconnected via the network (150). In the example of FIG. 1, the first pair of terminal devices (110) and (120) perform a one-way transmission of data. For example, the terminal device (110) may code video data (e.g., a stream of video data captured by the terminal device (110)) for transmission to another terminal device (120) via the network (150). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (120) may receive the coded video data from the network (150), decode the coded video data to recover video pictures, and display the video pictures according to the recovered video data. One-way data transmission may be common, such as in media serving applications.

[0015] In another example, the communication system (100) includes a second pair of terminal devices (130) and (140) performing bidirectional transmission of coded video data that may occur, for example, during a video conference. For the bidirectional transmission of data, each of the terminal devices (130) and (140) may code video data (e.g., a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (130) and (140) over the network (150). Each of the terminal devices (130) and (140) may also receive coded video data transmitted by the other of the terminal devices (130) and (140), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device in accordance with the recovered video data.

[0016] In the example of FIG. 1, the terminal devices (110), (120), (130), and (140) may be represented as a server, a personal computer, and a smartphone, although the principles of the present disclosure may not be so limited. The embodiments of the present disclosure find use with laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. The network (150) represents any number of networks that convey coded video data between the terminal devices (110), (120), (130), and (140), including, for example, wireline and / or wireless communication networks. The communication network (150) may exchange data in circuit-switched and / or packet-switched channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For the purposes of this discussion, the architecture and topology of the network (150) may be irrelevant to the operation of the present disclosure, unless otherwise described below.

[0017] 2 depicts the arrangement of a video encoder and a video decoder in a streaming environment as an example application of the disclosed subject matter. The disclosed subject matter can be similarly applicable to other video-enabled applications including, for example, video conferencing, digital TV, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0018] The streaming system may include a capture subsystem (213) that may include, for example, a video source (201), e.g., a digital camera, that generates a stream of uncompressed video pictures (202). In an example, the stream of video pictures (202) includes samples taken by the digital camera. The stream of video pictures (202) is represented by a bold line to emphasize its high data volume compared to the encoded video data (204) (or coded video bitstream), which may be processed by an electronic device (220) that includes a video encoder (203) coupled to the video source (201). The video encoder (203) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (204) (or encoded video bitstream (204)) is represented by a thin line to emphasize its lower data volume compared to the stream of video pictures (202), which may be stored in a streaming server (205) for future use. One or more streaming client subsystems, such as the client subsystems (206) and (208) of FIG. 2, can access the streaming server (205) to retrieve copies (207) and (209) of the encoded video data (204). The client subsystem (206) can include a video decoder (210), for example in an electronic device (230). The video decoder (210) decodes an incoming copy (207) of the encoded video data and generates an outgoing stream (211) of video pictures that can be rendered on a display (212) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (204), (207), and (209) (e.g., a video bitstream) can be encoded according to a particular video coding / compression standard.An example of such a standard is ITU-T Recommendation H.265. In an example, the video coding standard under development is colloquially known as Versatile Video Coding (VVC). The disclosed subject matter may be used in conjunction with VVC.

[0019] It is noted that electronic devices 220 and 230 can include other components (not shown). For example, electronic device 220 can include a video decoder (not shown), and electronic device 230 can similarly include a video encoder (not shown).

[0020] 3 shows a block diagram of a video decoder (310) according to an embodiment of the present disclosure. The video decoder (310) may be included in an electronic device (330). The electronic device (330) may include a receiver (331) (e.g., a receiving circuit). The video decoder (310) may be used in place of the video decoder (210) of FIG. 2.

[0021] The receiver (331) may receive one or more coded video sequences to be decoded by the video decoder (310), one coded video sequence at a time, in the same or other embodiments, where the decoding of each coded video sequence is independent of the other coded video sequences. The coded video sequences may be received from a channel (301), which may be a hardware / software link to a storage device that stores the encoded video data. The receiver (331) may receive the encoded video data together with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to their respective use entities (not shown). The receiver (331) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (315) may be coupled between the receiver (331) and the entropy decoder / parser (320) (hereinafter "parser (320)"). In certain applications, the buffer memory (315) is part of the video decoder (310). In others, it can be external to the video decoder (310) (not shown). In still others, there may be a buffer memory (not shown) external to the video decoder (310), e.g., to combat network jitter, plus another buffer memory (315) within the video decoder (310), e.g., to manipulate playback timing. When the receiver (331) is receiving data from a storage / forwarding device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (315) may not be needed or may be small. For use with best-effort packet networks such as the Internet, the buffer memory (315) may be needed, and may be relatively large and advantageously adaptively sized, and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (310).

[0022] The video decoder (310) may include a parser (320) for reconstructing symbols (321) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (310) and information for controlling a rendering device, such as a render device (312) (e.g., a display screen), which is not an essential part of the electronic device (330) but may be coupled to the electronic device (330) as shown in FIG. 3. The control information for the rendering device may take the form of a Supplementary Enhancement Information (SEI) message or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (320) may parse / entropy decode the received coded video sequence. The coding of the coded video sequence may follow a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, context-dependent or non-context-dependent arithmetic coding, etc. The parser (320) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the group. The subgroups may include Groups of Pictures (GOP), pictures, tiles, slices, macroblocks, coding units (CU), blocks, transform units (TU), prediction units (PU), etc. The parser (320) may also extract quantization parameter values, motion vectors, etc. from the coded video sequence information, such as transform coefficients.

[0023] The parser (320) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (315) to generate symbols (321).

[0024] The reconstruction of symbols (321) can have a wide variety of units depending on the type of coded video picture or portion thereof (e.g., inter and intra pictures, inter and intra blocks) and other factors. Which units are included and how may be controlled by subgroup control information parsed by the parser (320) from the coded video sequence. The flow of such subgroup control information between the parser (320) and the following units is not shown for clarity.

[0025] Beyond the functional blocks already mentioned, the video decoder (310) may be conceptually subdivided into a number of functional units, which are described below. In an actual implementation operating under commercial constraints, many of these units may interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, the following conceptual subdivision into functional units is adequate.

[0026] The first unit is a scalar / inverse transform unit (351), which receives the quantized transform coefficients as symbols (321) from the parser (320) along with control information including what to transform to use, block size, quantization factor, quantization scaling matrix, etc. The scalar / inverse transform unit (351) can output blocks containing sample values ​​that can be input to an aggregator (355).

[0027] In some cases, the output samples of the scaler / inverse transformer (351) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (352). In some cases, the intra-picture prediction unit (352) generates a block of the same size and shape as the block being reconstructed using surrounding already reconstructed information fetched from a current picture buffer (358). The current picture buffer (358) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. The aggregator (355) adds, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (352) to the output sample information provided by the scaler / inverse transformer unit (351).

[0028] In other cases, the output samples of the scalar / inverse transform unit (351) may relate to an inter-coded and potentially motion-compensated block. In such cases, the motion compensated prediction unit (353) may access the reference picture memory (357) to fetch samples used for prediction. After motion compensating the fetched samples according to the symbols (321) related to the block, the samples may be added by the aggregator (355) to the output of the scalar / inverse transform unit (351) (in this case referred to as residual samples or residual signals) to generate output sample information. The addresses in the reference picture memory (357) from which the motion compensated prediction unit (353) fetches prediction samples may be controlled by motion vectors available to the motion compensated prediction unit (353), for example in the form of symbols (321), which may have X, Y, and reference picture components. Motion compensation can also include interpolation of sample values ​​fetched from the reference picture memory (357) when sub-sample accurate motion vectors are used, as well as motion vector prediction mechanisms.

[0029] The output samples of the aggregator (355) may be subjected to various loop filtering techniques in the loop filter unit (356). Video compression techniques may include in-loop filter techniques that are controlled by parameters contained in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (356) as symbols (321) from the parser (320), but may also be responsive to meta-information obtained during decoding of previous portions (in decoding order) of the coded picture or coded video sequence, and may even be responsive to previously constructed loop filtered sample values.

[0030] The output of the loop filter unit (356) can be a sample stream that can be output to a render device (312) and further stored in a reference picture memory (357) for use in future inter-picture prediction.

[0031] Once a particular coded picture is fully reconstructed, it may be used as a reference picture for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (320)), the current picture buffer (358) may become part of the reference picture memory (357), and any unused current picture buffer may be reallocated before beginning reconstruction of a subsequent coded picture.

[0032] The video decoder (310) may perform decoding operations according to a given video compression technique in a standard, such as ITU-T Recommendation H.265. The coded video sequence may conform to a syntax prescribed by the video compression technique or standard in use, in the sense that the coded video sequence conforms to both the syntax of the video compression technique or standard and a profile documented in the video compression technique or standard. In particular, a profile may select a particular tool from all tools available in the video compression technique or standard as the optimal tool available for use under that profile. Also, for compliance, the complexity of the coded video sequence must be within the bounds defined by the level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples / second), maximum reference picture size, etc. The limits set by the level may in some cases be further limited through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management signaled in the coded video sequence.

[0033] In an embodiment, the receiver (331) may receive additional (redundant) data along with the encoded video. The additional data may also be included as part of the coded video sequence. The additional data may be used by the video decoder (310) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may take the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0034] 4 shows a block diagram of a video encoder (403) according to an embodiment of the present disclosure. The video encoder (403) is included in an electronic device (420). The electronic device (420) includes a transmitter (440) (e.g., a transmission circuit). The video encoder (403) may be used in place of the video encoder (203) in the example of FIG. 2.

[0035] The video encoder (403) may receive video samples from a video source (401) (which is not part of the electronic device (420) in the example of FIG. 4) that may capture video images to be coded by the video encoder (403). In other examples, the video source (401) is part of the electronic device (420).

[0036] The video source (401) may provide a source video sequence to be encoded by the video encoder (403) in the form of a digital video sample stream that can be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, etc.), any color space (e.g., BT.601 YCrCB, RGB, etc.), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (401) may be a storage device that stores previously prepared video. In a video conferencing system, the video source (401) may be a camera that captures local image information as a video sequence. The video data may be provided as multiple individual pictures that, when viewed in sequence, impart motion. The picture itself may be organized as a spatial array of pixels, each of which may have one or more samples depending on the sampling structure, color space, etc. in use. Those skilled in the art can easily understand the relationship between pixels and samples. The remainder of this specification focuses on samples.

[0037] According to an embodiment, the video encoder (403) may code and compress pictures of a source video sequence into a coded video sequence (443) in real-time or under any other time constraint required by the application. Imposing an appropriate coding rate is one function of the controller (450). In some embodiments, the controller (450) controls and is operatively coupled to other functional units as described below. Coupling is not shown for clarity. Parameters set by the controller (450) may include parameters related to rate control (picture skip, quantizer, lambda value for rate-distortion optimization techniques, etc.), picture size, group-of-picture (GOP) layout, maximum motion vector search range, etc. The controller (450) may be configured with other appropriate functions related to the video encoder (403) optimized for a particular system design.

[0038] In some embodiments, the video encoder (403) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (430) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (433) embedded in the video encoder (403). The decoder (433) reconstructs the symbols to generate sample data in a similar manner that the (remote) decoder will also generate (any compression between the symbols and the coded video stream is lossless in the video compression techniques contemplated in the disclosed subject matter). The reconstructed sample stream (sample data) is input to a reference picture memory (434). Since the decoding of the symbol stream produces bit-exact results independent of the location of the decoder (local or remote), the content in the reference picture memory (434) is also bit-perfect between the local and remote encoders. That is, the prediction part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder will "see" when using the prediction during decoding. This basic principle of reference picture synchronicity (and the resulting drift when synchronicity cannot be maintained, e.g., due to channel errors) is also used in several related technologies.

[0039] The operation of the "local" decoder (433) can be the same as a "remote" decoder, such as the video decoder (310), already described in detail above in conjunction with Figure 3. Referring also momentarily to Figure 3, however, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (445) and parser (320) can be lossless, the entropy decoding portion of the video decoder (310), including the buffer memory (315) and parser (320), may not be implemented entirely in the local decoder (333).

[0040] An observation that can be made at this point is that any decoder techniques, except for parsing / entropy decoding, present in the decoder do not necessarily have to be present in substantially the same functional form in the corresponding encoder. For this reason, the disclosed subject matter focuses on the operation of the decoder. A description of the encoder techniques may be omitted, in that they are the inverse of the decoder techniques described generically. Only to certain extents are more detailed descriptions required, which are given below.

[0041] In operation, in some examples, the source coder (430) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from the video sequence designated as "reference pictures." In this manner, the coding engine (432) codes differences between pixel blocks of the input picture and pixel blocks of the reference pictures that may be selected as predictive references for the input picture.

[0042] The local video decoder (433) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols generated by the source coder (430). The operation of the coding engine (432) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 4), the reconstructed video sequence may usually be a copy of the source video sequence with some errors. The local video decoder (433) may reproduce the decoding process that may be performed by the video decoder on the reference pictures, causing the reconstructed reference pictures to be stored in the reference picture cache (434). In this way, the video encoder (403) may locally store copies of reconstructed reference pictures that have common content with the reconstructed reference pictures that would be obtained by the far-end video decoder (without transmission errors).

[0043] The predictor (435) may perform a prediction search for the coding engine (432). That is, for a new picture to be coded, the predictor (435) may look for certain metadata, such as reference picture motion vectors, block shapes, or sample data (as candidate reference pixel blocks) from the reference picture memory (534) that may be suitable prediction references for the new picture. The predictor (435) may operate on a sample block-by-pixel block basis to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (435), the input picture may have prediction references derived from multiple reference pictures stored in the reference picture memory (434).

[0044] The controller (450) may manage the coding operations of the video coder (430), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0045] The output of all the above functional units may undergo entropy coding in an entropy coder (445), which converts the symbols produced by the various functional units into a coded video sequence by losslessly compressing the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0046] The transmitter (440) may buffer the coded video sequence produced by the entropy coder (445) to prepare it for transmission over a communication channel (460), which may be a hardware / software link to a storage device that will store the encoded video data. The transmitter (440) may merge the coded video data from the video coder (430) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0047] The controller (450) may manage the operation of the video encoder (403). During coding, the controller (450) may assign a particular coded picture type to each coded picture, which may affect the coding technique that may be applied to each picture. For example, pictures may often be assigned as one of the following picture types:

[0048] An Intra Picture (I-picture) may be a picture that can be coded and decoded without using any other picture in a sequence as a source of prediction. Some video codecs allow various types of Intra pictures, including, for example, Independent Decoder Refresh (IDR) pictures. Those skilled in the art are aware of such variations of I-pictures and their respective applications and characteristics.

[0049] A Predictive Picture (P-picture) may be a picture that can be coded and decoded by intra-prediction or inter-prediction using at most one motion vector and reference index to predict sample values ​​of each block.

[0050] A Bi-directionally Predictive Picture (B-picture) may be a picture that can be coded and decoded by intra- or inter-prediction using at most two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple-predictive picture(s) can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0051] A source picture may generally be spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples, respectively) and coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to each picture of the block. For example, blocks of I pictures may be non-predictively coded or they may be predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of P pictures may be predictively coded by spatial prediction with reference to one previously coded reference picture or by temporal prediction. Blocks of B pictures may be predictively coded by spatial prediction with reference to one or two previously coded reference pictures or by temporal prediction.

[0052] The video encoder (403) may perform coding operations according to a given video coding technique or standard, such as ITU-T Recommendation H.265. During its operation, the video encoder (403) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax defined by the video coding technique or standard being used.

[0053] In an embodiment, the transmitter (440) may transmit additional data along with the encoded video. The source coder (430) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other types of redundant data such as redundant pictures and slices, SEI messages or VUI parameter set fragments, etc.

[0054] A video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits correlation (temporal or other) between pictures. In an example, a particular picture being encoded / decoded, called the current picture, is divided into blocks. If a block in the current picture is similar to a reference block in a previously coded reference picture in the video that is still buffered, then that block in the current picture may be coded by a vector called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0055] In some embodiments, bi-prediction techniques may be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures are used, e.g., a first reference picture and a second reference picture, both preceding in decoding order (but may be past and future, respectively, in display order) the current picture in the video. A block in the current picture may be coded with a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. The block is predictable by a combination of the first and second reference blocks.

[0056] Furthermore, merge mode techniques can be used in inter-picture prediction to improve coding efficiency.

[0057] According to some embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed in units of blocks. For example, according to the HEVC standard, a picture in a sequence of video pictures is divided into coding tree units (CTUs) for compression, and the CTUs in a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU includes three coding tree blocks (CTBs), one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels can be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed to determine a prediction type for the CU, such as an inter-prediction type or an intra-prediction type. The CU is partitioned into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In an embodiment, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. Taking a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values ​​(e.g., luma values), such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0058] 5 shows a diagram of a video encoder (503) according to another embodiment of the present disclosure. The video encoder (503) is configured to receive a processed block of sample values ​​(e.g., a predictive block) in a current video picture included in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. In an example, the video encoder (503) is used in place of the video encoder (203) in the example of FIG. 2.

[0059] In an HEVC example, the video encoder (503) receives a matrix of sample values ​​for a processing block, such as a prediction block of 8x8 samples. The video encoder (503) determines whether the processing block is best coded in intra-mode, inter-mode, or bi-predictive mode, for example using rate-distortion optimization. If the processing block is to be coded in intra-mode, the video encoder (503) may use intra-prediction techniques to encode the processing block into a coded picture, and if the processing block is to be coded in inter-mode or bi-predictive mode, the video encoder (503) may use inter-prediction or bi-prediction techniques, respectively, to encode the processing block into a coded picture. In certain video coding techniques, the merge mode can be an inter-picture prediction sub-mode in which motion vectors are derived from one or more motion vector predictors without benefit of coded motion vector components outside the predictors. In certain other video coding techniques, there may be motion vector components applicable to the current block. In examples, the video encoder (503) includes other components, such as a mode decision module (not shown) that determines the mode of the processing blocks.

[0060] In the example of FIG. 5, the video encoder (503) includes an inter-encoder (530), an intra-encoder (522), a residual calculator (523), a switch (526), ​​a residual encoder (524), a general controller (521), and an entropy encoder (525), coupled as shown in FIG. 5.

[0061] The inter-encoder (530) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in a previous picture and a subsequent picture), generate inter-prediction information (e.g., a description of residual information according to an inter-encoding technique, motion vectors, merge mode information), and calculate an inter-prediction result (e.g., a prediction block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the encoded video information.

[0062] The intra encoder (522) is configured to receive samples of a current block (e.g., a processing block), in some cases compare the block to previously coded blocks in the same picture, and generate transformed quantized coefficients and, in some cases, intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). In an example, the intra encoder (522) also calculates an intra prediction result (e.g., a prediction block) based on the intra prediction information and a reference block in the same picture.

[0063] The generic controller (521) is configured to determine generic control data and control other components of the video encoder (503) based on the generic control data. In an example, the generic controller (521) determines the mode of the block and provides a control signal to the switch (526) based on the mode. For example, if the mode is an intra mode, the generic controller (521) controls the switch (526) to select an intra mode result for use by the residual calculator (523), and controls the entropy encoder (525) to select intra prediction information and include the intra prediction information in the bitstream. If the mode is an inter mode, the generic controller (521) controls the switch (526) to select an inter prediction result for use by the residual calculator (523), and controls the entropy encoder (525) to select inter prediction information and include the inter prediction information in the bitstream.

[0064] The residual calculation unit (523) is configured to calculate a difference (residual data) between the received block and a prediction result selected from the intra-encoder (522) or the inter-encoder (530). The residual encoder (524) is configured to operate on the residual data to encode the residual data to generate transform coefficients. In an example, the residual encoder (524) is configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various embodiments, the video encoder (503) also includes a residual decoder (528). The residual decoder (528) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (522) and the inter-encoder (530) as appropriate. For example, the inter-encoder (530) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (522) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are suitably processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

[0065] The entropy encoder (525) is configured to format a bitstream to include the encoded block. The entropy encoder (525) is configured to include various information in accordance with an appropriate standard, such as the HEVC standard. In an example, the entropy encoder (525) is configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other appropriate information in the bitstream. It should be noted that there is no residual information when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode in accordance with the disclosed subject matter.

[0066] 6 shows a diagram of a video decoder (610) according to another embodiment of the present disclosure. The video decoder (610) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In an example, the video decoder (710) is used in place of the video decoder (210) in the example of FIG. 2.

[0067] In the example of FIG. 6, the video decoder (610) includes an entropy decoder (671), an inter decoder (680), a residual decoder (673), a reconstruction module (674), and an intra decoder (672), coupled as shown in FIG.

[0068] The entropy decoder (671) may be configured to reconstruct from the coded picture certain symbols that represent the syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra- or inter-prediction information) that may identify the mode in which the block is coded (e.g., intra- or bi-prediction mode in merge or other submodes), the specific samples or metadata used for prediction by the intra decoder (672) or the inter decoder (680), respectively, residual information, e.g., in the form of quantized transform coefficients, etc. In an example, if the prediction mode is an inter or bi-prediction mode, the inter prediction information is provided to the inter decoder (680), and if the prediction type is an intra prediction type, the intra prediction information is provided to the intra decoder (672). The residual information may undergo inverse quantization and is provided to the residual decoder (673).

[0069] The inter decoder (680) is configured to receive the inter prediction information and to generate inter prediction results based on the inter prediction information.

[0070] The intra decoder (672) is configured to receive the intra prediction information and to generate a prediction result based on the intra prediction information.

[0071] The residual decoder (673) is configured to perform inverse quantization to retrieve inverse quantized transform coefficients and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (673) may also require certain control information (to include quantization parameters (QPs)), which may be provided by the entropy decoder (671) (datapath not shown since this is only low volume control information).

[0072] The reconstruction module (674) is configured to combine the residual output by the residual decoder (673) and the prediction result (possibly output by an inter- or intra-prediction module) in the spatial domain to form a reconstructed block. The reconstructed block may be part of a reconstructed picture, which in turn may be part of a reconstructed video. It is noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0073] It is understood that the video encoders (203), (403), and (503) and the video decoders (210), (310), and (610) may be implemented using any suitable technology. In some embodiments, the video encoders (203), (403), and (503) and the video decoders (210), (310), and (610) may be implemented using one or more integrated circuits. In other embodiments, the video encoders (203), (403), and (503) and the video decoders (210), (310), and (610) may be implemented using one or more processors executing software instructions.

[0074] Merge candidates may be formed by checking motion information from either spatial or temporal neighboring blocks of the current block. Referring to FIG. 7, the current block (701) has samples that are found by the encoder / decoder during the motion search process to be predictable from a previous block of the same size that is spatially shifted. Instead of directly coding its motion vector, the motion vector may be derived from metadata associated with one or more reference pictures, for example, from the most recent reference picture (in decoding order) using a motion vector associated with any one of five surrounding samples, denoted D, A, C, B, and E (702 to 706, respectively). Blocks A, B, C, D, and E may be referred to as spatial merge candidates. These candidates may be sequentially put into a merge candidate list. A pruning operation may be performed to ensure that duplicate candidates are removed from the list.

[0075] Block-based compensation from different pictures may be called motion compensation. Block compensation may also be done from previously reconstructed areas in the same picture, which may be called intra-picture block compensation, Intra Block Copy (IBC), or Current Picture Referencing (CPR). For example, a displacement vector indicating the offset between the current block and the reference block is called a block vector. According to some embodiments, the block vector points to a reference block that has already been reconstructed and is available for referencing. Also, considering parallel processing, reference areas beyond tile / slice boundaries or wavefront ladder-shaped boundaries may be excluded from being referenced by the block vector. Due to these constraints, the block vector may be different from the motion vector in motion compensation. The motion vector can be any value (positive or negative in either x or y direction).

[0076] Coding of block vectors may be either explicit or implicit. In the explicit mode, sometimes called Advanced Motion Vector Prediction (AMVP) in inter-coding, the difference between a block vector and its predictor is signaled. In the implicit mode, the block vector is recovered from the block vector's predictor in a similar manner to the motion vector in merge mode. The resolution of the block vector is limited to integer positions in some embodiments. In other embodiments, the resolution of the block vector may be allowed to point to fractional positions.

[0077] The use of intra block copy at the block level may be signaled using a block level flag called the IBC flag. In one embodiment, the IBC flag is signaled if the current block is not coded in merge mode. The IBC flag may also be signaled by a reference index approach, which is performed by treating the current decoded picture as a reference picture. In HEVC Screen Content Coding (SCC), such a reference picture is placed at the last position of the list. This special reference picture may also be merged with other temporal reference pictures in the DPB. IBC may also include variants such as inverted IBC (e.g., a reference block is flipped horizontally or vertically before being used to predict the current block), or line-based IBC (e.g., each compensation unit in an M×N coding block is an M×1 or 1×N line).

[0078] FIG. 8 illustrates an embodiment of intra-picture block compensation (e.g., intra-block copy mode). In FIG. 8, a current picture 800 includes a set of block regions that have already been coded / decoded (i.e., gray squares) and a set of block regions that are yet to be coded / decoded (i.e., white squares). One block 802 of the block regions that are yet to be coded / decoded may be associated with a block vector 804 that points to another block 806 that has been previously coded / decoded. Thus, any motion information associated with the block 806 may be used for coding / decoding the block 802.

[0079] In some embodiments, the search range of the CPR mode is constrained to be within the current CTU. The effective memory requirement for storing reference samples for the CPR mode is one CT size sample. Considering the existing reference sample memory to store reconstructed samples in the current 64x64 region, three more 64x64 size reference sample memories are required. The embodiments of the present disclosure extend the effective search range of the CPR mode to a part of the left CTU, while the total memory requirement for storing reference pixels remains unchanged (one CTU size, four 64x64 reference sample memories in total).

[0080] 9A-9D show examples of CTUs 900 and 902, each having four regions. CTU 902 is to the left of CTU 900, and each of the four regions of CTU 902 has been previously decoded. FIGS. 10A-10D show an embodiment of a reference sample memory with entries [1]-[4] corresponding to the size of one CTU. The reference sample memory may store reference samples of previously decoded CTUs for future IBC references. For example, when CTU 902 is decoded, entries [1]-[4] of the reference sample memory are filled with samples from the four regions of CTU 902, with entry [1] corresponding to the top left region, entry [2] corresponding to the top right region, entry [3] corresponding to the bottom left region, and entry [4] corresponding to the bottom right region. When an entry of the reference sample memory is filled, it then contains samples available for future IBC references.

[0081] In FIG. 9A, the top left region of the CTU 900 is the current region being decoded. When the top left region of the CTU 900 is decoded, entry [1] of the reference sample memory is overwritten with a sample from this region, as represented in FIG. 10A (e.g., the overwritten memory location has diagonal cross-hatching). In FIG. 9B, the top right region of the CTU 900 is the next current region being decoded. When the top right region of the CTU 900 is decoded, entry [2] of the reference sample memory is overwritten with a sample from this region, as represented in FIG. 10B. In FIG. 9C, the bottom left region of the CTU 900 is the next current region being decoded. When the bottom left region of the CTU 900 is decoded, entry [3] of the reference sample memory is overwritten with a sample from this region, as represented in FIG. 10C. In FIG. 9D, the bottom right region of the CTU 900 is the next current region being decoded. When the bottom right region of CTU 900 is decoded, entry [4] of the reference sample memory is overwritten with the sample from this region, as represented in FIG. 10D.

[0082] The embodiments of the present disclosure improve IBC performance under certain reference area constraints, such as when the size of the reference sample memory is constrained. In some embodiments, the size of the reference sample memory is constrained to 128×128 luma samples (and corresponding chroma samples). In an example, one CTU size of the reference sample is considered as the specified memory size. Further examples include different memory size / CTU size combinations, such as 64×64 luma samples (and corresponding chroma samples) for the CTU size and 128×128 luma samples (and corresponding chroma samples) for the memory size.

[0083] FIG. 11 illustrates example CTUs 1100 and 1102. As illustrated in FIG. 11, CTU 1102 is to the left of CTU 1100 and includes four previously decoded regions. CTU 1100 is the current CTU being decoded, with the top left region having been decoded. The top right region of CTU 1100 is the current region being decoded, and block 1104 is the current block in the top right region being decoded. Block 1104 may have three reference blocks 1106A-1106C. As illustrated in FIG. 11, each of reference blocks 1106A-1106C is located in CTU 1102 to the left of CTU 1100. Each of blocks 1106A-1106C has a block 1108A-1108C, respectively, at the same location in CTU 1100.

[0084] According to some embodiments, a co-located block refers to a pair of blocks having the same size, one block in a previously coded CTU and the other block in a current CTU. For example, if the memory buffer size is 1 CTU, the previous CTU means a CTU offset by 1 CTU-wide luma sample to the left of the current CTU. Moreover, these two blocks have the same position offset value with respect to the top-left corner of their own CTU, respectively. In this respect, a pair of co-located blocks is two blocks that have the same y coordinate with respect to the top-left corner of the picture, but different CTU widths in x coordinates (i.e., two co-located blocks have the same position coordinates within each CTU). For example, in FIG. 11, the reference block 1106A and its co-located block 1108A have the same x, y coordinates in CTUs 1102 and 1100, respectively. Similarly, reference block 1106B and its co-located block 1108B have the same x, y coordinates in CTUs 1102 and 1100, respectively. Furthermore, reference block 1106C and its co-located block 1108C have the same x, y coordinates in CTUs 1102 and 1100, respectively.

[0085] In Fig. 11, the size of the reference sample memory is assumed to be one CTU. Thus, the reference block 1106C can be found in the reference sample memory because the corresponding co-located block 1108C in the current CTU has not yet been decoded (this is demonstrated by the co-located block 1108C being located in a white area). Thus, the location in the reference sample memory corresponding to the reference block 1106C still stores a reference sample from the left CTU.

[0086] In contrast to reference block 1106C, reference block 1106A cannot be used because the corresponding co-located block 1108A in CTU 1100 has been reconstructed (i.e., decoded) (this is demonstrated by the co-located block 1108A being located in a grey area). Thus, the location in the reference sample memory for reference block 1106A has been updated with reference samples from CTU 1100 and is therefore no longer available. Similarly, reference block 1106B is not a valid reference block to be used for decoding because the corresponding co-located block 1108B in CTU 1100 has been reconstructed and therefore the location in the reference sample memory for reference block 1106B has been updated with data in CTU 1100.

[0087] According to some embodiments, a reference block in a previously decoded CTU is available to be used for IBC lookup if its corresponding co-located block in the current CTU has not yet been reconstructed. In some embodiments, the co-located sample in the current CTU of the top left corner sample of the reference block is checked. If the co-located sample in the current CTU has not yet been reconstructed, the rest of the reference block is available for IBC lookup. In some embodiments, when the memory size is one CTU, referring to a previously decoded CTU means referring to the CTU immediately to the left of the current CTU.

[0088] When the memory size is larger than the CTU (e.g., a reference sample memory of size 2 CTUs is allowed), the previously coded CTU references the CTU to the left of the CTU to the left of the current CTU, as shown in Figure 12. For example, in Figure 12, CTU 1200 is the current CTU being decoded, and CTUs 1202 and 1204 are two previously decoded CTUs to the left of CTU 1200. Block 1204 is the current block being decoded, and reference block 1206 is the reference block for current block 1204. Furthermore, block 1208 is co-located with block 1206. However, in this example, the x-coordinate offset between blocks 1206 and 1208 is twice the CTU width.

[0089] According to some embodiments, the following conditions apply: Formula 1: (yCb+(mvL0[1]>>4))>>CtbLog2SizeY=yCb>>CtbLog2SizeY Formula 2: (yCb+(mvL0[1]>>4)+cbHeight-1)>>CtbLog2SizeY=yCb>>CtbLog2SizeY Formula 3: (xCb+(mvL0[0]>>4))>>CtbLog2SizeY>=(xCb>>CtbLog2SizeY)-1 Formula 4: (xCb+(mvL0[0]>>4)+cbWidth-1)>>CtbLog2SizeY>=(xCb>>CtbLog2SizeY)-1

[0090] Equations 1-4 may be used to find the reference block. Equations 1 and 2 mean that the top and bottom of the reference block should be in the same CTU row. Equations 3 and 4 mean that the left and right of the reference block should be in the current or left CTU. In the above equations, xCb and yCb are the x and y coordinates of the current block, respectively. The variables cbHeight and cbWidth are the height and width of the current block, respectively. The variable CtbLog2SizeY refers to the CTU size in log2 domain. For example, CtbLog2SizeY=7 means the CTU size is 128x128. The variables mvL0[0] and mvL0[1] refer to the x and y components of the block vector mvL0, respectively.

[0091] According to some embodiments, when it is determined that the reference block of the current block is in a different CTU than the current CTU of the current block, the reference sample memory is checked to determine whether samples corresponding to the reference block are available. In some embodiments, determining whether the reference block is in a different CTU than the current CTU is determined as follows: Formula 5: (xCb+(mvL0[0]>>4))>>CtbLog2SizeY=(xCb>>CtbLog2SizeY)-1

[0092] In the case where a reference block of a current block is in a different CTU than the CTU of the current block, determining whether a sample of the reference block is available in the reference memory may, according to some embodiments, include as input: (i) the x and y coordinates of the current block (xCb, yCb), and (ii) Adjacent luma position ((xCb+(mvL0[0]>>4)+(1<<CtbLog2SizeY),yCb+(mvL0[1]> >4))) is determined using

[0093] If the output is false, the sample of the reference block is determined to be available. For example, for a current block at a current position (xCb, yCb), inputs (i) and (ii) are used to determine whether a neighboring block (xNb, yNb) is available to the current block. Available means that the block has already been decoded and can be used for intra prediction (e.g., within the same tile).

[0094] According to some embodiments, when the reference block of the current block is in a different CTU than the CTU of the current block, M ×2 N The region of M is checked to determine whether the samples of the reference block are available in the reference sample memory. M and N may be positive integers. M ×2 N Determining whether a region of is available in the reference memory may, according to some embodiments, include as input: (i) the x and y coordinates of the current block (xCb, yCb), and (ii) Adjacent luma position (((xCb+(mvL0[0]>>4)+(1<<CtbLog2SizeY))> >(CtbLog2SizeY-1))<<(CtbLog2SizeY-1),((yCb+(mvL0[1]>>4))>>(CtbLog2SizeY-1))<<(CtbLog2SizeY-1)) is determined using

[0095] If the output is false, the samples of the reference block are determined to be available (e.g., the neighboring block is available for use in intra block copying). For example, if M and M are equal to 8, and any sample of a 64×64 region in the current CTU (called the current sample) is being reconstructed, then the corresponding 64×64 region in the reference sample memory in which the co-located sample of the current sample is located is not available for IBC reference. As such, the reference sample memory may be updated on a 64×64 basis.

[0096] In some embodiments, the CTUs in a picture have variable sizes where the difference in width or height is doubled or halved. When the CTU size is reduced by half, the reference sample memory that previously stored one CTU stores four CTUs in this case. Thus, instead of two CTUs to the left of the current CTU as shown in FIG. 12, there are four CTUs to the left of the current CTU. In these scenarios, i.e., 4-CTU reference data or 2-CTU reference data, all other previously coded samples in other CTUs to the left of the current CTU, except for the leftmost CTU, are fully available without using the condition check in the above embodiment. For the leftmost CTU, the condition check in the above embodiment is similar for the availability of reference samples, but the adjustment of the x-coordinate offset is 2×CTU width if there are two CTUs in the leftmost CTU, and 4×CTU width if there are four CTUs in the leftmost CTU.

[0097] 13 and 14 depict embodiments of a process used in the reconstruction of a block coded in intra mode to generate a prediction block for the block being reconstructed. In various embodiments, the process is performed by a processing circuit such as the processing circuit of the terminal devices (110), (120), (130), and (140), a processing circuit performing the function of the video encoder (203), a processing circuit performing the function of the video decoder (210), a processing circuit performing the function of the video decoder (310), a processing circuit performing the function of the intra prediction module (352), a processing circuit performing the function of the video encoder (403), a processing circuit performing the function of the predictor (435), a processing circuit performing the function of the intra encoder (522), a processing circuit performing the function of the intra decoder (672), etc. In some embodiments, the process is implemented in software instructions, such that the processing circuit performs the process when the processing circuit executes the software instructions.

[0098] The process may generally begin at step S1300 where a coded video bitstream is received. The process proceeds to step S1302 where it is determined whether a reference block for a current block is in a different CTU than the current CTU of the current block. If it is determined that the reference block is not in a different CTU, the process proceeds to S1304 where IBC is performed on the current block using the reference block.

[0099] If it is determined that the reference block is in a different CTU, the process proceeds from step S1302 to step S1306, where it is determined whether the CTU of the current block and the reference sample memory have the same size. If the CTU of the current block and the reference sample memory are not the same size, the process proceeds to process A, which is described in more detail below. If the CTU of the current block and the reference sample memory are the same size, the process proceeds to step S1308, where a first area is determined for the current CTU. By way of example, the first area may be the area of ​​the reference block, i.e., 2 M ×2 N A block may be co-located with the region, where M and N are positive integers.

[0100] The process proceeds to step S1310, where it is determined whether a memory location for the reference block is available. For example, a first area located in the current CTU may be co-located with a second area in a different CTU. In the different CTU, the second area includes the reference block. If the first area is at least partially reconstructed, it is determined that the memory location for the reference block in the reference sample memory is unavailable. If it is determined that the memory location in the reference sample memory for the reference block is unavailable, the process proceeds to step S1312, where a default process is performed, such as selecting another reference block. Alternatively, if it is determined that the memory location in the reference sample memory for the reference block is unavailable, the default process can be to place a predefined value for forming a reference block for the current block, such as 1<<(bit_depth-1), where bit_depth is the depth of bits used per sample. If the memory location in the reference sample memory for the reference block is available, the process proceeds from step S1310 to step S1314, where one or more samples are read from the memory location corresponding to the reference block to decode the current block. Process A may generally begin at step S1400, where it is determined whether the size of the CTU of the current block is smaller than the size of the reference sample memory. If the size of the CTU of the current block is not smaller than the size of the reference sample memory, the process proceeds to step S1402 to determine whether a memory location for the reference block in the reference sample memory is available. For example, steps S1308-S1312 may be repeated at step S1402, as described above.

[0101] If in step S1400 it is determined that the size of the CTU of the current block is smaller than the size of the reference sample memory, the process proceeds to step S1404, where it is determined whether the distance between the different CTU in which the reference block is located and the current CTU in which the current block is located is smaller than a threshold value. As an example, the distance between the reference block and the current block may be determined based on the difference between the X coordinates of these blocks. As an example, the threshold value may be ((reference sample memory size / CTU size)-1) x (CTU width) may be defined as:

[0102] If the distance between the different CTU of the reference block and the CTU of the current block is less than the threshold, the process proceeds to step S1406 to read one or more samples for decoding the current block from a memory location corresponding to the reference block. At this point, if the distance between the reference block of the different CTU and the current block is less than the threshold, the memory check described in steps S1308 to S1312 of FIG. 13 is not performed. If the distance between the reference block of the different CTU and the current block is equal to or greater than the threshold, the process returns from step S1404 to step S1402. The process depicted in FIG. 14 ends after step S1402 or S1404.

[0103] The scenario of Figure 14 is represented in Figure 12 where the size of the reference sample memory is twice as large as the size of the current CTU. If the reference block is located in CTU1202, the distance between CTU1202 and the current CTU is less than a threshold value. Therefore, in this scenario, a memory check of the reference sample memory is not required since the memory location in the reference sample memory corresponding to the reference block is available. If the reference block is located in CTU1204, the distance between CTU1204 and the current CTU is greater than or equal to a threshold value. Therefore, in this scenario, the memory check described in steps S1308-S1312 of Figure 13 is performed to determine whether the memory location is available.

[0104] The above techniques can be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, Figure 15 illustrates a computer system (1400) suitable for implementing certain embodiments of the disclosed subject matter.

[0105] The computer software may be coded in any suitable machine code or computer language that may be subject to mechanisms such as assembly, compilation, linking, etc. to generate code including instructions that may be executed by one or more central processing units (CPUs), graphics processing units (GPUs), etc., directly or through interpretation, microcode execution, etc.

[0106] The instructions may be executable by various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming consoles, devices for the Internet of Things, and the like.

[0107] 15 for computer system (1400) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of computer system (1400).

[0108] The computer system (1400) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more users through, for example, tactile input (e.g., keyboard, swipes, dataglove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), and olfactory input (not shown). The human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., speech, music, ambient sounds), images (e.g., scanned images, photographic images obtained from a still camera), and video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

[0109] The input human interface devices may include one or more (only one of each is shown) of a keyboard (1401), a mouse (1402), a trackpad (1403), a touch screen (1410), a data glove (not shown), a joystick (1405), a microphone (1406), a scanner (1407), and a camera (1408).

[0110] The computer system (1400) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the user's senses, for example, through haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (1410), data gloves (not shown), or joystick (1405), although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers (1409), headphones (not shown)), visual output devices (e.g., screens (1410) including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which may provide two-dimensional visual output or output in more than three dimensions, such as by means of stereoscopic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0111] The computer system (1400) may also include human accessible storage devices and their associated media, such as CD / DVD ROM / RW (1420) with CD / DVD or similar media (1421), thumb drives (1422), removable hard disks or solid state drives (1423), legacy magnetic media such as tapes and floppy disks (not shown), dedicated ROM / ASIC / PLD based devices such as security dongles (not shown), and the like.

[0112] Those skilled in the art will also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not include transmission media, carrier waves, or other transitory signals.

[0113] The computer system (1400) may also include interfaces to one or more communication networks. The networks may be, for example, wireless, wireline, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., TV wireline or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicle and factory networks including CAN bus, etc. Certain networks generally require an external network interface adapter attached to a particular general purpose digital port or peripheral bus (1449) (e.g., a USB port of the computer system (1400)). Others are generally built into the core of the computer system (1400) by attachment to a system bus as described below (e.g., an Ethernet network to a PC computer system, or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (1400) may communicate with other entities. Such communications may be one-way receive-only (e.g., broadcast TV) or one-way transmit-only (e.g., a CAN bus to a specific CAN bus device), or may be two-way, for example, to other computer systems using local or wide area digital networks. Specific protocols or protocol stacks may be used with each of the networks and network interfaces as described above.

[0114] The above-mentioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (1440) of the computer system (1400).

[0115] The cores (1440) may include one or more central processing units (CPUs) (1441), graphics processing units (GPUs) (1442), dedicated programmable processing units in the form of field programmable gate arrays (FPGAs) (1443), hardware accelerators (1444) for specific tasks, etc. These devices may be connected through a system bus (1448), along with read only memory (ROM) (1445), random access memory (RAM) (1446), internal mass storage such as an internal non-user accessible hard drive, SSD, etc. (1447). In some computer systems, the system bus (1448) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripherals may be attached directly to the core's system bus (1448) or through a peripheral bus (1449). Architectures for peripheral buses include PCI, USB, etc.

[0116] The CPU (1441), GPU (1442), FPGA (1443), and accelerator (1444) can execute certain instructions that, in combination, may constitute the above computer code. The computer code may be stored in a ROM (1445) or a RAM (1446). Temporary data may also be stored in the RAM (1446), while persistent data may be stored, for example, in an internal mass storage device (1447). Rapid storage and retrieval from any of the memory devices may be made possible by the use of a cache memory. A cache memory may be closely associated with one or more of the CPU (1441), GPU (1442), mass storage device (1447), ROM (1445), RAM (1446), etc.

[0117] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those of ordinary skill in the computer software arts.

[0118] By way of example, and not by way of limitation, a computer system having the architecture (1400), and in particular the core (1440), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be media associated with the user-accessible mass storage devices introduced above, in addition to specific storage of the core (1440) that is non-transitory in nature, such as the core's internal mass storage (1447) or ROM (1445). Software implementing various embodiments of the present disclosure can be stored in such devices and executable by the core (1440). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (1440), and in particular the processor (including a CPU, GPU, FPGA, etc.) therein, to perform certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (1446) and modifying such data structures according to processes defined by the software. Additionally or alternatively, the computer system may provide functionality as a result of logic implemented by hardware or otherwise embodied in circuitry (e.g., accelerator (1444)) that may operate in place of or in conjunction with software to perform certain processes or portions of certain processes described herein. References to software may encompass logic, and vice versa, where appropriate. References to computer-readable media may encompass circuitry (e.g., integrated circuits (ICs)) that store software for execution, circuitry that embodies logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0119] Appendix A: Acronyms JEM: joint exploration model VVC:versatile video coding BMS:benchmark set MV:Motion Vector HEVC:High Efficiency Video Coding SEI:Supplementary Enhancement Information VUI:Video Usability Information GOP:Group(s) of Pictures TU:Transform Unit(s) PU:Prediction Unit(s) CTU:Coding Tree Unit(s) CTB:Coding Tree Block(s) PB:Prediction Block(s) HRD:Hypothetical Reference Decoder SNR:Signal Noise Ratio CPU:Central Processing Unit(s) GPU:Graphics Processing Unit(s) CRT:Cathode Ray Tube LCD:Liquid-Crystal Display OLED:Organic Light-Emitting Diode CD:Compact Disc DVD:Digital Video Disc ROM:Read-Only Memory RAM:Random Access Memory ASIC:Application-Specific Integrated Circuit PLD:Programmable Logic Device LAN:Local Area Network GSM: Global System for Mobile communications LTE: Long Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCT:Peripheral Component Interconnect FPGA:Field Programmable Gate Areas SSD: Solid-State Drive IC: Integrated Circuit CU: Coding Unit

[0120] While this disclosure has described several example embodiments, there are alterations, permutations, and various substitute equivalents that are within the scope of this disclosure. Thus, it will be apparent to those skilled in the art that numerous systems and methods will be able to embody the principles of the present disclosure and thus be within its spirit and scope, even if not explicitly shown or described herein.

[0121] (1) A method of video decoding for a decoder, comprising: receiving a coded video bitstream; determining whether a reference block for a current block is located in a coding tree unit (CTU) different from a CTU of the current block, the reference block and the current block being located in the same picture included in the coded video bitstream; in response to determining that the reference block is located in the different CTU, determining whether the CTU of the current block and a reference sample memory have the same size; in response to determining that the CTU of the current block and the reference sample memory have the same size, (i) determining a first area in the CTU of the current block that is co-located with a second area in the different CTU, the first area having position coordinates in the CTU of the current block that are the same as position coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location of the reference sample memory for the reference block is available based on a decoding status of the first area; and (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from the memory location corresponding to the reference block; The method according to claim 1,

[0122] (2) The method according to feature (1), wherein the first area is the current block and the second area is the reference block.

[0123] (3) Each of the first area and the second area is 2 M ×2 N The method according to any one of features (1) or (2), wherein the size is

[0124] (4) The method according to feature (3), wherein M=6 and N=6.

[0125] (5) A method according to any one of features (1) to (4), wherein in response to determining that the decoding status of the first area indicates that the first area does not include at least one block that is at least partially decoded, the memory location corresponding to the reference block is determined to be available.

[0126] (6) in response to determining that the reference sample memory and the CTU of the current block are not the same size, determining whether a size of the CTU of the current block is smaller than a size of the reference sample memory; in response to determining that a size of the CTU of the current block is smaller than a size of the reference sample memory, determining whether a distance between the different CTU of the reference block and the CTU of the current block is smaller than a threshold defined as ((reference sample memory size / CTU size)-1) x (CTU width); in response to determining that the distance is less than the threshold, reading from the memory location corresponding to the reference block one or more samples for decoding the current block; The method according to any one of features (1) to (5), further comprising:

[0127] (7) in response to determining that the distance is greater than or equal to the threshold, (i) determining a first area in the CTU of the current block that is co-located with a second area in the different CTU, the first area having position coordinates in the CTU of the current block that are the same as position coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location of the reference sample memory for the reference block is available based on a decoding status of the first area; and (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from the memory location corresponding to the reference block; The method according to feature (6), further comprising:

[0128] (8) A video decoder for video decoding, comprising: A processing circuit is provided, the processing circuit comprising: receiving a coded video bitstream; determining whether a reference block for a current block is located in a coding tree unit (CTU) different from a CTU of the current block, the reference block and the current block being located in a same picture included in the coded video bitstream; in response to determining that the reference block is located in the different CTU, determining whether the CTU of the current block and a reference sample memory have the same size; in response to determining that the CTU of the current block and the reference sample memory have the same size, (i) determining a first area in the CTU of the current block that is co-located with a second area in the different CTU, the first area having position coordinates in the CTU of the current block that are the same as position coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location of the reference sample memory for the reference block is available based on a decoding status of the first area; (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from the memory location corresponding to the reference block. It is configured as follows: Video decoder.

[0129] (9) The video decoder according to feature (8), wherein the first area is the current block and the second area is the reference block.

[0130] (10) Each of the first area and the second area is 2 M ×2 N 2. A video decoder according to claim 1, having a size of

[0131] (11) A video decoder according to feature (10), wherein M=6 and N=6.

[0132] (12) A video decoder according to any one of features (8) to (11), wherein in response to determining that the decoding status of the first area indicates that the first area does not include at least one block that is at least partially decoded, it is determined that the memory location corresponding to the reference block is available.

[0133] (13) The processing circuit includes: in response to determining that the reference sample memory and the CTU of the current block are not the same size, determining whether a size of the CTU of the current block is less than a size of the reference sample memory; in response to determining that a size of the CTU of the current block is smaller than a size of the reference sample memory, determining whether a distance between the different CTU of the reference block and the CTU of the current block is less than a threshold defined as ((reference sample memory size / CTU size)-1) x (CTU width); In response to determining that the distance is less than the threshold, reading one or more samples for decoding the current block from the memory location corresponding to the reference block.

[0023] A video decoder according to any one of features (8) to (12).

[0134] (14) The processing circuit includes: in response to determining that the distance is greater than or equal to the threshold value; (i) determining a first area in the CTU of the current block that is co-located with a second area in the different CTU, the first area having position coordinates in the CTU of the current block that are the same as position coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location of the reference sample memory for the reference block is available based on a decoding status of the first area; (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from the memory location corresponding to the reference block.

[0023] A video decoder according to feature (13).

[0135] (15) A non-transitory computer-readable medium storing instructions, comprising: The instructions, when executed by a processor of a video decoder, cause the processor to: receiving a coded video bitstream; determining whether a reference block for a current block is located in a coding tree unit (CTU) different from a CTU of the current block, the reference block and the current block being located in the same picture included in the coded video bitstream; in response to determining that the reference block is located in the different CTU, determining whether the CTU of the current block and a reference sample memory have the same size; in response to determining that the CTU of the current block and the reference sample memory have the same size, (i) determining a first area in the CTU of the current block that is co-located with a second area in the different CTU, the first area having position coordinates in the CTU of the current block that are the same as position coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location of the reference sample memory for the reference block is available based on a decoding status of the first area; and (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from the memory location corresponding to the reference block; 4. A method comprising: Non-transitory computer-readable medium.

[0136] (16) The non-transitory computer-readable medium according to feature (15), wherein the first area is the current block and the second area is the reference block.

[0137] (17) Each of the first area and the second area is 2 M ×2 N 16. A non-transitory computer-readable medium according to claim 15, having a size:

[0138] (18) The non-transitory computer-readable medium according to any one of features (15) to (17), wherein in response to determining that the decoding status of the first area indicates that the first area does not include at least one block that is at least partially decoded, the memory location corresponding to the reference block is determined to be available.

[0139] (19) The method further comprises: in response to determining that the reference sample memory and the CTU of the current block are not the same size, determining whether a size of the CTU of the current block is smaller than a size of the reference sample memory; in response to determining that a size of the CTU of the current block is smaller than a size of the reference sample memory, determining whether a distance between the different CTU of the reference block and the CTU of the current block is smaller than a threshold defined as ((reference sample memory size / CTU size)-1) x (CTU width); in response to determining that the distance is greater than the threshold, reading one or more samples for decoding the current block from the memory location corresponding to the reference block; Further comprising A non-transitory computer-readable medium according to any one of features (15) to (18).

[0140] (20) The method further comprises: in response to determining that the distance is greater than or equal to the threshold value; (i) determining a first area in the CTU of the current block that is co-located with a second area in the different CTU, the first area having position coordinates in the CTU of the current block that are the same as position coordinates of the second area in the different CTU of the reference block; (ii) determining whether a memory location of the reference sample memory for the reference block is available based on a decoding status of the first area; and (iii) in response to determining that the memory location for the reference block is available, reading one or more samples for decoding the current block from the memory location corresponding to the reference block; It further has: A non-transitory computer-readable medium according to feature (19).

[0141] [Incorporated by reference] This disclosure claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 791,862, entitled "REFERENCE SAMPLE MEMORY REUSE FOR INTRA PICTURE BLOCK COMPENSATION," filed on January 13, 2019, which claims the benefit of priority to U.S. Provisional Patent Application No. 16 / 502,822, entitled "METHOD AND APPARATUS FOR REFERENCE SAMPLE MEMORY REUSE FOR INTRA PICTURE BLOCK COMPENSATION," filed on July 3, 2019. The entire disclosures of these prior applications are incorporated herein by reference in their entireties.

Claims

1. 1. A method of video decoding performed by a decoder, comprising: receiving a coded video bitstream; determining whether a reference block for a current block is located in a different coding tree unit (CTU) than a CTU of the current block, the reference block and the current block being located in a picture that is part of the coded video bitstream; if the reference block is located in the different CTU, determining whether a size of the CTU of the current block is smaller than a size of a reference sample memory; When the size of the CTU of the current block is smaller than the size of the reference sample memory, determining whether the distance between the different CTU of the reference block and the CTU of the current block is less than or equal to a threshold determined by ((reference sample memory size / CTU size)-1) x (CTU width); if the distance is less than or equal to the threshold, reading one or more samples for decoding the current block from a memory location in the reference sample memory that corresponds to the reference block; The method according to claim 1,

2. If the distance is greater than the threshold, or if the size of the CTU of the current block is not smaller than the size of the reference sample memory, (i) determining a first area in the CTU of the current block that is co-located with a second area in the different CTU, the first area and the second area having the same location in the CTU of the current block and the different CTU of the reference block; (ii) determining whether the memory location of the reference sample memory for the reference block is available based on a decoding status of the first area; (iii) reading one or more samples for decoding the current block from the memory location corresponding to the reference block if the memory location for the reference block is available; The method of claim 1 further comprising:

3. the first area is the current block; The second area is the reference block. The method of claim 2.

4. Each of the first area and the second area is Ｍ ×2 Ｎ having a size The method of claim 2.

5. M=6 and N=6; The method according to claim 4.

6. the memory location corresponding to the reference block is determined to be available if the decoding status of the first area indicates that the first area does not include at least one block that has been at least partially decoded.

6. The method according to any one of claims 2 to 5.

7. A video decoding device for video decoding, comprising: A processing circuit configured to implement the method according to any one of claims 1 to 6 by reading and executing instructions stored in a memory. Video decoding device.

8. When executed by a processor of a video decoder, the processor A computer program for carrying out the method according to any one of claims 1 to 6.

9. 1. A method of video encoding performed by an encoder, comprising: coding a video bitstream; receiving the coded video bitstream; determining whether a reference block for a current block is located in a different coding tree unit (CTU) than a CTU of the current block, the reference block and the current block being located in a picture that is part of the coded video bitstream; if the reference block is located in the different CTU, determining whether a size of the CTU of the current block is smaller than a size of a reference sample memory; When the size of the CTU of the current block is smaller than the size of the reference sample memory, determining whether the distance between the different CTU of the reference block and the CTU of the current block is less than or equal to a threshold determined by ((reference sample memory size / CTU size)-1) x (CTU width); if the distance is less than or equal to the threshold, reading one or more samples for decoding the current block from a memory location in the reference sample memory that corresponds to the reference block; The method according to claim 1,

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